Bad vegetable oils

What are harmful or poor quality vegetable oils?

What vegetable oils are harmful?

There is a belief that all vegetable oils are healthy, either because they come from plant-based foods, or because they have a high content of unsaturated fats. However, neither the plant origin, nor the type of fats that the oils contain, assure us that they are good for health: that the oils are beneficial, they have to come from good quality oils.

There are many vegetable oils that are healthy but are really harmful.

Why is there a belief that all oils are healthy?

olive oil market
Virgin olive oils in a Spanish market. This oil is internationally recognized for being the healthiest.

It is always said that oils are healthy because they provide omega 3 and omega 6 fatty acids. These types of fats are only found in vegetables (walnuts, flax, chia, sunflower…) and in the oils that are extracted from these .

The importance of omega fats is that they must be provided in the diet because the body is not able to manufacture them. For this reason they are classified as essential fatty acids. (On the other hand, the body is capable of producing omega 9 or saturated fat from carbohydrates, for example). However, the great nuance found in these types of omega fats are only healthy if they come from quality oils or healthy foods.

Omega fats from refined oils are damaged by the temperatures to which they have been subjected, which causes the body to have a prooxidant effect.

How can an oil be bad or harmful?

Currently we find that oils may be providing more inconvenience than advantages in food, mainly for these reasons:

  • Refined oils are mainly consumed, whose refining process has deteriorated the fats and these are transformed into pro-oxidants
  • Heating and fried oils are consumed, forming, at high temperatures, potentially toxic compounds in the oil
  • Too many seed oils are consumed, too polyunsaturated, which deteriorate easily (even if they are virgin)
  • There is an imbalance in omega 6 and omega 3 fats in the diet

Why are refined oils harmful?

The refining consists of heating the oleaginous fruits and adding solvents so that they release all the oil that it still contains, after the cold pressure. It is a good system to take advantage of all the oil of the fruits, but it is not the most ideal for health.

Refined oils should not usually be consumed because during this process these oils deteriorate and lose vitamin E and the flavonoids that these oils contain, losing their antioxidant properties and becoming a pro-oxidant of the body. In addition, during the refining, the fats they contain also deteriorate (which increases acidity).

What is a  good vegetable oil?

Oil acidity label
Example of “bad” refined oil: it advertises as “soft flavor” as if it had a positive appearance, but in reality it means that it contains refined oils and therefore greater acidity and less properties.

A good vegetable oil for health is the the so-called virgin oil or an oil extracted by cold pressure.

We must pay attention to the label because this information is very important and often appears misleading or hidden. When the bottle indicates a certain degree of acidity, it means that it contains refined oils (regulations may depend on each country).

Problems of heated oils

We have already learned to buy healthy oils, which are virgins or sought by cold pressure, but now we have another problem: we should not heat them.

When the oils overheat, the properties of the oil deteriorate and toxic substances are produced. In general, the recommendation would be not to eat too much heated oil and use only the necessary oils for frying. (See: Disadvantages of heated oils)

Harmful seed oils

Harmful and healthy oils
Harmful and healthy oils main characteristics

In the food stores you can find different oils with a different composition. To summarize, not all oils have a healthy composition: those richer in polyunsaturated fats are worse because they degrade more easily. This is why sunflower oil gets spoilt more easily than olive oil

The best to do is to use oils rich in oleic acid, such as virgin olive oil, and obtain polyunsaturated fats (omega) from eating rich foods, such as walnuts or ground flax or chia seeds. (See: What is the best type of oil?)

Imbalance in omega 6 and omega 3 fats in the diet

The consequence of ingesting too many seed oils, such as sunflower oil, is that they are very rich in omega 6. This causes an imbalance in the body’s balance between omega 3 and omega 6: the excess of omega 6 blocks the effects of omega 3, which is usually deficient in the diet, increasing inflammation.

punto rojo More information on vegetable oils

This article was endorsed by Elisenda Carballido - Dietitian nutritionist. Postgraduate in Phytotherapy and master in Nutrition and Metabolism.
Written by Editorial Botanical-online team in charge of content writing

2 January, 2022

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